Manufacture of molds used for casting metal pipes and the like by the centrifugal method



Dec. 7, 1937. VAN 2,101,726

MANUFACTURE OF MOLDS USED FOR CASTING METAL PIPES A AND THE LIKE BY THE CENTRIFUGAL METHOD A Filed Oct. 7, 1935,

Patented Dec. 7, i937 UNITED STATES PATENT OFFICE lNG 'METAL PIPES AND THE LIKE BY THE GENTBJFUGAL METHOD Antonius J. van Z iip, Kaarlem, Netherlands, assignor to. Koninklijke Nederlandsche Boogovens en Staalfabrieken Netherlands a N. V., Hmuiden,

Application October 1, 1935, Serial No. 43,954

In the Netherlands October 11, 193i 2Glaims.

This invention relates to an improved method of lining a long,'cylindrical flask with sand. In accordance with common practice, the flask is 'placed in vertical position, whereupon a core formed by'amodel or pattern of the pipe to be cast is lowered into the flask and centered, and a stream of sand is fed to the interspace between said elements. During the sand filling, the flask with the core are sometimes kept in light vibra tion to further the descent of the sand to the lower end of the mold.

With a view to ensuring the required compactness of the sand lining for withstanding the pressure exerted thereon during centrifugal casting, the sand in the mold is compressed either radially, or axially.

In the'first case, viz. radial compression, the I core is given a smaller diameter than the pipe to be cast, but is provided at its'lower end with a conical shoulder merging, beyond the space for receiving the molding sand, into a cylindrical head having an outer diameter corresponding with that of, said pipe. After the sand fillin the core is raised, whereby the sand is radially compressed in, all directions by said shoulder I and head.

I In the second case, viz. axial compression, the core has the exact size of the pipe and is after the sand filling subjected, together with the flask, to a strong bumping action by means of a jolting apparatus adapted to alternately lift the mold through a small distance and allow it to drop.

Both said methods are in a way suitable for the purpose, but neither ensures good results without exception. With both methods it may occur that after the centrifugal castingoperation the external diameter of the cast pipe is somewhat too great, or the outer face of the pipe is irregular'in other respects. The lining near the ends of the mold, however, has always been found to have suflicient compactness, especially when the second method has been employed.

A minute research with the aid of a special testing machine has now revealed the fact that towards the middle of the mold the hardness, i. e. the compactness of the sand lining rather rapidly decreases to a value that may not be sufficient for all conditions, and if the sand has also been rammed at the top end, it may even be that the hardness first increases, and thereafter still ness graph, in such a manner that, after suitable treatment of. the mold in the jolter, substantially the sand lining to be perfectly uniform through out. the length of the mold,,it ordinarily suflices to aproximate the correct shape of the model,

in such manner that the end sections of the core are cylindrical and have the same outer diameter as the pipe to be cast, whereas the central section is also cylindrical but has a somewhat smaller diameter, said cylindricalsections joining one another through slightly conical portions. During the axial shifting of the core through the flask, the hardness of the sand lining at the ends retains its initial value. In the central portion, however, the compactness of the lining increases in accordance with the ratio between the diameters before and after the shifting of the core, respectively. By means of the above testing apparatus it has been shown that in a mold thus manufactured the compactness of the lining is always and in any point amply suflicient for withstanding the centrifugal pressure.

If the sand, after being fed to the interspace between flask and core and treated .by the jolter, should not or only insufficiently be rammed at the top, its compactness also at that end might not be suflicient under all conditions. In that case, also the top section of the model would have to be thinner than the pipe to be cast, but this has the inconvenience that no stripping ring can be used when the core is raised. As compared with the aforesaid known method "of radial compression, the method in accordance with the invention has the further advantage that, owing to the action of the jolter-prior to the raising of the core, it is possible under all conditions to ensure a sufficiently known initial compactness throughout the length of the mold. This is not the case with, the prior method, for vibration of the mold during the inflow of the .sand does not warrant a uniform initial compactne'ss of the lining.

On the drawing. Fig. 1 represents, in a sectional elevation, a vertically placed flask for centrifugal casting, in cooperation with the model to be used in practicing my novel method. Fig. 2 illustrates hardness graphs of the lining.

Placed within the iron flask l and accurately centered in relation thereto is the model, the

sections 2, 4 and 6 of which are cylindrical, the intermediate sections 3 and 5 having the shape of truncated cones. The diameters of the cylindrical end sections 2 and 6 are equal to the outer diameter of the pipe to be cast, whereas the diameter of the central section 4 is somewhat smaller. Said sections merge into one another through the conical sections 3 and 5.

At the lower end, the core has a reduced portion 1 extending through the pattern 8 for the socket of the pipe to be cast, said portion being adapted to be secured to the support 9 of the diagrammatically shown jolter l0.

Provided vertically above the mold is-a guide tube H for the molding sand, which is supplied by a distributing apparatus 12. Arranged within the tube ll there is an annular weight I3, which carries at its lower end a pattern ll for the spigot of the pipe to be cast, and which itself is suspended from cables I5. The weight I3 is adapted to be locked in its uppermost position, so that the sand from the distributor may freely flow down into the space between the tube l2 and the weight l3. At its top, the core is provided with a knob I6, by means of which it can be raised and lowered.

After the space between the flask and the core has been packed with molding sand, the supply of sand is cut off and the mold is subjected to the action of the jolter l0, whereby the sand is axially compressed by its own gravity. Thereafter, and if necessary for the purpose, an additional amount of sand is supplied and the mold again jolted, whereupon the jolter is stopped and some blows are imparted to the sand by means of the weight l3 so as to further compress the lining.

Determination of the hardness of the sand lining by means of the above testing apparatus results into a. graph as shown by a full line in Fig. 2. From this graph it will appear that the hardness of the lining near the ends of the mold is ample, but that in the central portion it is not quite suihcient to withstand the centrifugal pressure of the molten metal. If the core in accordance with my invention is now axially shifted through the flask, during which operation the weight l3 functions as a stripping ring, the sand is compressed only in the portion intermediate the ends, in such a manner that a substantially uniform compactness throughout the length of the mold is obtained, somewhat as shown by the dash-and-dot line in the diagram.

What I claim is:-

1. Method of manufacturing a mold for casting metal pipes and similar objects by the use of a flask and a former therein, consisting in filling sand into the space around the former, then packing the sand first by jolting, then by ramming and finally by radial compression.

2. In a pipe molding apparatus the combination with an upright flask, of a former extending therethrough and provided with cylindrical end sections of the same diameter as the finished article, a cylindrical middle section of smaller diameter and intermediary sections gradually tapering from the larger to the smaller sections, a jolting device at the lower end of the former, a hopper for sand at the upper end of the flask, an annular ram in said hopper fitting loosely around the upper end of the former and means for axially displacing said former; whereby, while the flask is being filled with sand from the hopper, the sand becomes compressed in axial direction of the apparatus by the jolting device and finally radially compressed upon displacement of said former.

ANTONIUS J. VAN ZIJP. 

